I have an uncoated DPMS Stainless Steel lower receiver AR15. Is there any clear coating that I can use to protect the finish on this rifle? I would like to keep the natural SS color. I have been wiping it down with CLP and this seems to work OK but have heard from others that some rusting has occured on their SS receivers. How about a simple spray on polyurethane? The finish appears to be rough from the casting or perhaps bead blasted.